Re: [Caml-list] xpath or alternatives

["Mikkel Fahnøe Jørgensen" <mikkel@dvide.com>]

2009/9/30 Richard Jones <rich@annexia.org>:
> On Wed, Sep 30, 2009 at 01:00:15AM +0200, Mikkel Fahnøe Jørgensen wrote:
>> In line with what Yaron suggests, you can use a combinator parser.
> It's interesting you mention xmlm, because I couldn't write
> the code using xmlm at all.

If you can manage to convert an xml document into a json like tagged
tree structure,
then a simple solution like

module Value = struct
56	    type value_type =
57	      Object of (string * value_type) list
58	    | Array of value_type list
59	    | String of string
60	    | Int of int
61	    | Float of float
62	    | Bool of bool
63	    | Null
64	  end
65	
..
665	  let get_object v = match v with Object x -> x
666	    | _ -> fail "json object expected"
..
685     let pattern_path value names =
686	    let rec again value = function
687	      | "*" :: names  -> List.iter (fun (n, v) -> try again v names
688	          with Invalid_argument _ | Not_found -> ()) (get_object value)
689	      | name :: names -> again (List.assoc name (get_object value)) names
690	      | [] -> raise (Found value)
691	    in try again value names; raise Not_found with Found value -> value
692	

combined with a path split function

22	  let split c s =
23	    let n = String.length s in
24	    let rec again i lst =
25	      begin try let k = String.rindex_from s i c in
26	        again (k - 1) ((if i = k then "" else (String.sub s (k + 1)
(i - k))) :: lst)
27	        with _ -> (String.sub s 0 (i + 1)) :: lst
28	      end
29	    in again (n - 1) []

will do almost exactly what you are asking for - notice the "*"
searches broadly in all subtrees. You can add your own xpath like
functions as you discover a need for them.

I believe that the xmlm examples has a tree transformation operation
that would easily be adapted to produce a json like tree, if modified
a little.

let out_tree o t =
  let frag = function
  | E (tag, childs) -> `El (tag, childs)
  | D d -> `Data d
  in
  Xmlm.output_doc_tree frag o t


> My best effort, using xml-light, is around 40 lines:

If you spend those 40 lines on a layer on top of a lightweight xml
parser, you might get away with 3 lines the next time.